A magnetic particle testing method has been widely applied as a conventional quality assurance technique for a railway wheel (referred to simply as a wheel, hereinafter) including a hub, a plate, and a rim in sequence from inward to outward in the radial direction of the wheel.
As a magnetic particle testing apparatus for magnetic particle testing on a wheel, an apparatus disclosed in Patent Literature 1 has been known, for example.
The magnetic particle testing apparatus disclosed in Patent Literature 1, for the purpose of enabling to detect defects in any direction of the entire surface of the wheel, includes: a through conductor inserted into a bore (a hole of hub), and energized with direct current; and a pair of magnetizing coils so disposed as to face respective opposite side surfaces of the wheel, and energized with alternating current.
According to the magnetic particle testing apparatus disclosed in Patent Literature 1, the energized through conductor generates a magnetic flux extending in the circumferential direction of the wheel, which enables radial defects radially extending around the bore to be detected. In addition, each magnetizing coil generates a magnetic flux extending in the radial direction of the wheel, which enables circumferential defects concentrically extending around the bore to be detected.
In Patent Literature 1, defect detectability is evaluated using an A-type standard test specimen specified by JIS, and it is shown that magnetic particle patterns have been clearly observed.
Meanwhile, in Europe, BN918277 and EN13262 are known as manufacturing standards for a railway wheel. In BN918277, the magnetic flux density in space in the vicinity of each side surface of a wheel in a magnetized state is required to be 2.5 mT to 8.2 mT. In EN13262, the magnetic flux density in space in the vicinity of each side surface of a wheel in a magnetized state is required to be 4 mT or more.